Subaru vehicles are beloved for their boxer engines and symmetrical all-wheel drive, but they have unique systems and quirks that produce their own set of dashboard warnings. This guide covers the most common Subaru-specific warning lights and how to approach diagnosis.
Check Engine Light
Common triggers on Subaru vehicles include oxygen sensor faults (P0420 catalytic converter efficiency is extremely common on EJ-series boxer engines), knock sensor codes (the horizontally opposed engine layout makes these sensors more susceptible to vibration-related false readings), secondary air injection system faults (a common issue on 2000s-era Subarus), and EVAP purge valve failures. Read codes with an OBD-II scanner and refer to your Subaru workshop manual’s diagnostic flowcharts for the specific code.
AT TEMP Warning (CVT/Automatic)
Subaru uses Lineartronic CVT transmissions across most of its current range (Impreza, XV/Crosstrek, Forester, Outback, Liberty/Legacy). The AT TEMP light indicates the CVT fluid is overheating, typically during heavy load driving, towing, or sustained hill climbing. Pull over and let the transmission cool at idle in Park. Regular CVT fluid changes are essential – Subaru recommends their specific CVT fluid at intervals between 50,000 and 100,000 km depending on the model. Using non-Subaru CVT fluid can damage the transmission.
VDC Warning Light
Subaru uses VDC (Vehicle Dynamics Control) as its stability system. The VDC light flashing during slippery conditions is normal. If it stays on permanently, the most common cause is a wheel speed sensor fault. On Subaru models with the multiplate centre differential (WRX, STI, older Legacy GT), the VDC light can also be triggered by a failing centre differential duty solenoid or a rear differential preload issue. Your workshop manual includes the AWD system diagnostic procedures.
Cruise Control Flashing
On many Subaru models, a flashing cruise control light accompanies the check engine light as a secondary indicator. This is not a separate fault with the cruise control system – it is Subaru’s way of alerting you to the engine management fault. Diagnosing the check engine light code will resolve both warnings.
Oil Temperature Warning
Some Subaru models (particularly the turbo WRX and STI) have a dedicated oil temperature warning. The boxer engine layout, combined with a turbocharger, can cause high oil temperatures during spirited driving. If this light comes on, reduce engine load and let the oil temperature drop. Ensure you are using the correct oil grade (Subaru turbo engines typically require 5W-30 fully synthetic meeting Subaru specifications) and that the oil level is correct.
AWD Warning
An AWD warning light can indicate mismatched tyre sizes (even small differences in tread depth between front and rear can trigger this on Subaru’s AWD system), a faulty duty solenoid in the centre coupling, or low differential fluid. Subaru’s AWD system is sensitive to tyre diameter differences – always replace tyres in sets of four or ensure matched tread depths across all four wheels.
Diagnostic Resources
Subaru uses manufacturer-specific codes alongside standard OBD-II codes. Browse our Subaru workshop manual collection or search at mechanicmate.net/shop.
